1. Field of the Invention
This invention relates generally to etching systems and, more particularly, to an etching system and apparatus for controllably etching openings which have a minimum dimension that is on the order of or less than the thickness of the metal in which the opening is etched by use of a protective film which overlays a resist layer which is located on one surface of the continuous strip of metal and a plurality of etching stations which continuously spray etchant onto the continuously moving strip of metal.
2. Description of the Prior Art
In a typical television color tube, the shadow mask or aperture mask, as it is sometimes called, is located between the electron guns at the rear of the tube and phosphor coated faceplate at the front of the tube. Electron beams pass through the openings or apertures in the shadow mask and impinge upon a suitable color producing phosphor dot on the faceplate. Behind each of these openings in the shadow mask and on the faceplate are sets of three phosphor dots, a triad, one dot for each of the primary colors. Typically, around each of these dots is a black area which surrounds the various color phosphor dots. During the operation of the picture tube, the shadow mask openings or apertures act as a guide for the electron beams.
One of the problems in the manufacture of a television aperture mask is the difficulty in accurately manufacturing masks with the miniature or small openings therein. Recently, there has been a demand for a mask in which the opening is elongated with the width or the minimum dimension of the elongated openings being on the order of or less than the thickness of the material from which the mask is made. The problem of mass producing aperture masks having an opening with a dimension on the order of the thickness of the mask material is that to date it is difficult, if not impossible, to have a system and apparatus that will accurately and consistently etch openings which have a minimum dimension on the order of 0.007 inch to 0.002 inch when the base material is 0.006 inch to 0.009 inch. It has been found that the conventional mass production etching techniques, i.e., etching from both sides, are unacceptable because these techniques generally produce over-etching as well as irregular etching. The over-etching is produced by lateral etching of the base material that inherently accompanies etching perpendicular to the surface of the material. Consequently, the process of making apertures having a minimum dimension on the order of or less than the thickness of the material has to date been a difficult and time-consuming task as each aperture mask must be individually etched and checked to obtain a usable aperture mask.
Examples of technique for attempting to accurately etch an opening in very thin material are shown in the Kubo U.S. Pat. No. 3,679,500, assignees' prior art copending application U.S. Ser. No. 487,663 filed July 11, 1974 by Frantzen, Barton and Ring for "Etching Process for Accurately Making Small Holes in Thick Materials," and German Offenlengungsschrift Pat. No. 3,432,602 which shows the use of a roll of film. While all these prior art processes are useful teachings, the main problem of having a system that consistently and accurately etches small openings in a continuous strip of moving metal, remains as a difficult but desirable goal from both a quality and economic standpoint.
The present invention comprises an advancement to the art by disclosing an apparatus having metal web handling machines, a film applying machine which securely applies a protective layer over a moving metal web so that the web can be directed through a plurality of etching stations in which the etchant is sprayed on both sides of the metal web even though a protective film is located on one side of the metal web.